[raynor]

Let's say your race is a rock/oxygen race and you colonize a huge world that is rock/methane. So, this is a domed colony with only room for 5 facilities. Later in the game, you declare war on a race that is ice/methane. Eventually, they surrender to you. Now, you have one or more planets with colonists who breath methane.

Load these colonists onto a transport and send the transport to your huge rock/methane colony. Now, transfer some of these colonists down to the planet. Then, move all of your oxygen breathers back to the transport. The dome goes away, and you now can build 25 facilities on the huge world. This is much, much faster than waiting 25 for an Atmosphere Modifier III to convert the atmosphere.

If all goes well, you will eventually conquer races that breathe all four of the atmosphere types: Hydrogen, Oxygen, Carbon Dioxide and Methane. Unfortunately, you will still have to build Atmosphere Modifier Plants on any colonies with the atmosphere 'none'.

Hope this helps.